Three-dimensional lithography for rutile TiO₂ single crystals using swift heavy ions

We have developed a nano-micro structure fabrication method in rutile TiO₂ single crystal by use of swift heavy-ion irradiation. The area where ions heavier than Cl ion accelerated with MeV-order high energy were irradiated was well etched by hydrofluoric acid, by comparison etching was not observed in the pristine TiO₂ single crystal. Noticed that the irradiated area could be etched to a depth at which the electronic stopping power of the ion decayed to a value of 6.2keV/nm. We also found that the value of the electronic stopping power was increased, eventually decreased against depth in TiO₂ single crystal with, e.g. 84.5MeV Ca ion. Using such a beam, inside of TiO₂ single crystal was selectively etched with 20% hydrofluoric acid, while the top surface of TiO₂ single crystal subjected to irradiation was not etched. Roughness of the new surface created in the single crystal was within 7nm with the atomic forth microscopy measurement.